Need help selecting the right prop

[jteabo]

I need some help to select the right prop. See boat details below.

1) Performance issue you are trying to correct.
Trying to get a better hole-shot and get on a plane sooner.
Currently with average load its very difficult to get on a plane if I have more than 2 passengers. I often need to have passengers move towards the bow until I get on a plane.

2) Current prop manufacturer, model, aluminum or stainless and as a minimum.
Currently I have the stock prop which is aluminum, 3 blade

3) Current prop diameter and pitch (required).
Current prop is 19 pitch, and I think its a 14.5" diameter

4) Wide open throttle RPM and speed with an average load (very helpful)
My engine is rated 4400-4800 RPM (printed on the carb cover)
With average load the WTO currently is 4200-4400 RPM

5) Engine/drive make, model, year, and HP
1991 Mercruiser Alpha1 4.3L v6, 2 bbl, no EFI, sterndrive, 205 hp,

6) Boat make model, year, length and weight
1991 Freedom Marine, 19 ft, 2500 lb

I dont have any trim tabs on the boat, I trim with the sterndrive which has a stabilizer (Sting-Ray XP Hydrofoil) attached.
I am also looking at the Smart-Tabs to help with the hole-shot and getting on a plane.

I'm not sure if I should do the Smart-Tabs or the prop, or both.
I had a friend suggest a 15 pitch 4 blade prop, but I dont know if that is the best solution. Any advice is welcomed.

 

[usskydvr]

Re: Need help selecting the right prop

Drop down to a 17 pitch 3 blade.

 

[Tail_Gunner]

Re: Need help selecting the right prop

) Current prop diameter and pitch (required).
Current prop is 19 pitch, and I think its a 14.5" diameter

4) Wide open throttle RPM and speed with an average load (very helpful)
My engine is rated 4400-4800 RPM (printed on the carb cover)
With average load the WTO currently is 4200-4400 RPM


19@4300
18@4500
17@4700

can we go a bit deeper...17 on a 19' boat with a healthy 4.3 is a tad shy..Look at your outdrive on the lower part there is gear ratio..Could you post it and lose the hydrofoil..Its 70's stuf...

Ohh is the current prop ss or alum

 

[jteabo]

Re: Need help selecting the right prop

The prop is aluminum.
The gear ratio stamped on the sterndrive is: 1.84
And, the WOT with average load is 4200 RPM at about 34 MPH with current prop.

Should I get a 17 pitch 4 blade?

 

[Tail_Gunner]

Re: Need help selecting the right prop

Personally i would recomend that you have your motor looked at, Timing...plugs...fuel filter....carb a full tune up...and your hull is it free from any growth?.....maybe a compression test to

Let me give you a example 19' boat 3000lbs with a 4.3(205hp) 1.66 gears turns a 19p alum prop to 50 and a 21 to 54

So if i use the same slip factor and change the gearing to 1.84 in the example boat it would turn a 23p prop..odd thats the mfg rated prop size for that boat...

Im not trying to complicate things for you..Hmm I am certain if you tune the motor...drop the fin...add smart tabs..(Nauticus) you would get far better results...Tabs should eliminate that stern from dragging in the hole

 

[jteabo]

Re: Need help selecting the right prop

You were right. Had the carb rebuilt and replaced the fuel pump. New plugs, cap and rotor. Timed it and hit the water. Now it runs at WOT @ 4800 rpm and does 42 mph. Hole shot is faster and it planes sooner. Don't think I need to mess with the prop after all. Thanks for your help. the mech that rebuilt the carb said it was the dirtiest carb he ever saw.